Basic Oxygen Furnace (BOF) steelmaking produces, among other things, large amounts of carbon monoxide (CO) gas above the molten metal bath. This so called "off-gas" contains more potential heat than the total heat generated in the steel/slag bath by oxidation reactions. If this so called "post-combustion" heat, generated by the burning of CO to CO.sub.2 above the bath, can be recaptured by the steel bath, significant energy and cost savings can be achieved. By effectively recapturing the post-combustion heat larger amounts of scrap can be charged to the bath, which would result in higher steel production yields in hot-metal-limited BOF shops. Similarly, it would enable the refining of lower cost iron ore to decrease BOF steel costs in hot-metal-rich BOF shops. Unfortunately, with current BOF practices most of the potential heat energy from the off-gas is wasted due to inefficient heat transfer between the gas and the bath. Previous attempts to capture the post-combustion energy within the BOF vessel have typically resulted in premature vessel lining failure.
In addition to the various off-gases, BOF steelmaking practices also have the tendency to generate a foamy slag. While a small amount of foamy slag can have beneficial effects on the metallurgical reactions in the BOF, foamy slag is, by its nature, potentially hazardous and generally avoided. When large amounts of foam are produced, slopping of the foam from the BOF vessel can become uncontrollable, causing yield loss as well as environmental and safety hazards. As a result, there have been many efforts made to control or minimize the production of foamy slag. Despite the numerous problems associated with foamy slag, it has nevertheless been found that it can provide a good heat transfer medium between the post-combustion heat generated by the combustion of CO to CO.sub.2 and the bath. The percentage of heat generated by combusting CO gas to CO.sub.2 gas that is returned to the bath is known as the heat transfer efficiency.